Full Idea
A structure is a model of a sentence if the sentence is true in the model; a structure is a model of a set of sentences if they are all true in the structure.
Gist of Idea
A structure models a sentence if it is true in the model, and a set of sentences if they are all true in the model
Source
José L. Zalabardo (Introduction to the Theory of Logic [2000], §3.6)
Book Reference
Zalabardo,José L.: 'Introduction to the Theory of Logic' [Westview 2000], p.110